1. Field of the Invention
The present invention relates to a wirecut electrical discharge machine (EDM) for machining a workpiece using a wire electrode. In particular, the invention is a wirecut EDM utilizing a silicon powder in the dielectric to promote even electrical discharge so as to improve machining quality.
2. Description of the Related Art
Wirecut electrical discharge machines which employ a metal wire of approximately 0.05 to 0.3 mm in diameter as an electrode are well known. The electrode, which extends in a Z direction, is moved in X and Y directions relative to a workpiece so as to perform a machining operation on the workpiece due to electrical discharge energy generated between the electrode and the workpiece by a source of current.
In order to facilitate the electrical discharge, a dielectric fluid, such as water, is placed in a gap between the electrode and the workpiece. However, several disadvantages are present in such a system. Water becomes ionized when energy is passed through it by virtue of electrical discharge. Because of this ionization, arcs tend to be concentrated and not uniformly distributed across a workpiece. Also, a high conductivity sludge, consisting of particles machined from the workpiece, tends to collect around the area being machined. This phenomenon increases the conductivity of the dielectric where the sludge resides, and causes a greater proportion of the electrical discharge to occur at this location. The result is that more machining takes place midway through the workpiece in the thickness direction and a consistent cut or contour cannot be imparted to the workpiece. In addition, concentrated arcing tends to heat up the electrode at the portion thereof and increases the likelihood of breaking the electrode.
Kerosene and other petrochemicals have been utilized as a dielectric medium in an EDM process in an attempt to avoid ionization and create a more uniform distribution of electrical discharge along the workpiece. However, due to the relatively low conductivity of such media, the gap between the workpiece and the electrode must be very small. This introduces problems with breakage of the electrode due to contact with the workpiece as a result of vibrations and electric field forces inherent in the system. In addition, contact between the electrode and the workpiece adversely affects the quality of machining done to the workpiece.
Many conventional wirecut EDM systems utilize a single electrode for machining a number of identical workpieces that are arranged in parallel to each other. However, with such an arrangement, with water utilized as a dielectric, when an arc is developed at one workpiece, the voltage between the electrode and the other workpieces may be reduced to a point below the discharge voltage needed to accomplish machining, typically about 30 v. Accordingly, resistors are arranged in series with each workpiece so as to maintain an adequate voltage between each workpiece and the electrode. Since these resistors must have very high power ratings, such an arrangement adds considerable initial expense and maintenance costs to an EDM apparatus. Of course, if petroleum-based dielectrics are utilized, the above-mentioned limitations again become apparent, i.e., the low conductivity requires an undesirably small machining gap.
It is known that the use of silicon in the dielectric and electrode of EDM systems, other than the wirecut type, will increase surface hardness and corrosion resistance of a workpiece. Such a surface treatment is discussed in Progress of Electrical Discharge Machining, by Dr. Nagao Saito. However, it has not been previously proposed to utilize silicon in the dielectric of a wirecut EDM so as to facilitate the machining process.